Barrier materials for metal interconnect

ABSTRACT

A method is provided for manufacturing a semiconductor device by: depositing a tantalum layer to line the channels and vias of a semiconductor; depositing a tungsten nitride layer at a low temperature on the tantalum layer; and depositing a copper conductor layer on the tungsten nitride layer. The tungsten nitride acts as a highly efficient copper barrier material with high resistivity while the tantalum layer acts as a conductive barrier material to reduce the overall resistance of the barrier layer.

TECHNICAL FIELD

The present invention relates generally to semiconductors and morespecifically to barrier materials used in semiconductor processing.

BACKGROUND ART

In the process of manufacturing integrated circuits, after theindividual devices, such as the transistors, have been fabricated in thesilicon substrate, they must be connected together to perform thedesired circuit functions. This connection process is generally called"metalization", and is performed using a number of differentphotolithographic and deposition techniques.

One metalization process, which is called the "damascene" technique,starts with the placement of a first channel dielectric layer, which istypically an oxide layer, over the semiconductor devices. A firstdamascene step photoresist is then placed over the oxide layer and isphotolithographically processed to form the pattern of the firstchannels. An anisotropic oxide etch is then used to etch out the channeloxide layer to form the first channel openings. The damascene stepphotoresist is stripped and a barrier layer is deposited to coat thewalls of the first channel opening to ensure good adhesion and to act asa barrier material to prevent diffusion of such conductive material intothe oxide layer and the semiconductor devices (the combination of theadhesion and barrier material is collectively referred to as "barrierlayer" herein). A seed layer is then deposited on the barrier layer toform a conductive material base, or "seed", for subsequent deposition ofconductive material. A conductive material is then deposited in thefirst channel openings and subjected to a chemical-mechanical polishingprocess which removes the first conductive material above the firstchannel oxide layer and damascenes the conductive material in the firstchannel openings to form the first channels.

For multiple layers of channels, another metalization process, which iscalled the "dual damascene" technique, is used in which the channels andvias are formed at the same time. In one example, the via formation stepof the dual damascene technique starts with the deposition of a thinstop nitride over the first channels and the first channel oxide layer.Subsequently, a separating oxide layer is deposited on the stop nitride.This is followed by deposition of a thin via nitride. Then a via stepphotoresist is used in a photolithographic process to designate roundvia areas over the first channels.

A nitride etch is then used to etch out the round via areas in the vianitride. The via step photoresist is then removed, or stripped. A secondchannel dielectric layer, which is typically an oxide layer, is thendeposited over the via nitride and the exposed oxide in the via area ofthe via nitride. A second damascene step photoresist is placed over thesecond channel oxide layer and is photolithographically processed toform the pattern of the second channels. An anisotropic oxide etch isthen used to etch the second channel oxide layer to form the secondchannel openings and, during the same etching process to etch the viaareas down to the thin stop nitride layer above the first channels toform the via openings. The damascene photoresist is then removed, and anitride etch process removes the nitride above the first channels in thevia areas. A barrier layer is then deposited to coat the via openingsand the second channel openings. Next, a seed layer is deposited on thebarrier layer. This is followed by a deposition of the conductivematerial in the second channel openings and the via openings to form thesecond channel and the via. A second chemical-mechanical polishingprocess leaves the two vertically separated, horizontally perpendicularchannels connected by a cylindrical via.

The use of the damascene techniques eliminates metal etch and dielectricgap fill steps typically used in the metalization process. Theelimination of metal etch steps is important as the semiconductorindustry moves from aluminum to other metalization materials, such ascopper, which are very difficult to etch.

One drawback of using copper is that copper diffuses rapidly throughvarious materials. Unlike aluminum, copper also diffuses throughdielectrics, such as oxide. When copper diffuses through dielectrics, itcan cause damage to neighboring devices on the semiconductor substrate.To prevent diffusion, materials such as tantalum nitride (TaN), titaniumnitride (TiN), and tungsten nitride (WN) are used as barrier materialsfor copper. A thin layer of adhesion material, such as titanium, isfirst formed on the dielectrics or vias to ensure good adhesion and goodelectrical contact of the subsequently deposited barrier layer tounderlying doped region and/or conductive channels. Adhesion/barriermaterial stacks such as tantalum/tantalum nitride (Ta/TaN) andtitanium/titanium nitride (Ti/TiN) have been found to be useful asadhesion/barrier material combination for copper interconnects. In thecase of WN, it has been found that no adhesion layer is necessarybecause WN adheres well to dielectrics, such as oxide, and because it isan amorphous material making it a desirable barrier material for copperprocesses.

The "barrier effectiveness" of a barrier material layer with respect toa conductive material is its ability to prevent diffusion of theconductive material. The barrier effectiveness of a barrier materiallayer is determined in part by its thickness, including the thicknessuniformity, and its quality, including the number and sizes of defectssuch as pinholes which form on deposition. To resist copper diffusion,it is found that a minimum barrier material thickness of 5 nm isrequired. However, to minimize the electrical resistance due to thebarrier material layer, it is desirable to maintain a thin barriermaterial layer. Therefore, it is typical to keep the barrier materiallayer thickness close to about 5 nm. While it is generally easy tomaintain a minimum thickness of 5 nm at the bottom of the channels orvias, it is difficult to do so at the sidewalls of the channels or thevias. Occasionally, there may be insufficient barrier material thicknessat the sidewalls which would allow copper to diffuse through, causingdamages to adjacent devices.

Another important factor to the barrier effectiveness of a barriermaterial layer is its chemical composition. In the case of a WN barrierlayer, an increase in its nitrogen content increases its barriereffectiveness. A WN barrier layer with a higher nitrogen content ispreferred because the increase in barrier effectiveness compensates forthe thickness non-uniformity or presence of pinholes and makes the layermore robust in preventing diffusion of conductive material therethrough.However, an increase in the nitrogen content would also undesirablyincrease the electrical resistance of the barrier layer.

Another problem with using WN as a barrier material layer is that thecrystallographic texture of the overlying copper layer is poor whichmeans that it has poor resistance to electromigration of the copperwhich in turn leads to voids in the copper. Essentially, copper atoms inthe channels and vias tend to migrate with the flow of current and formvoids when the grains of the crystalline structure of the copper are notclosely aligned.

Even further, WN precludes using a low temperature process and the hightemperature made it difficult to integrate with many low k dielectricmaterials.

Generally, with higher resistivity materials such as WN, there have beentwo major problems. First they lead to high interface resistance betweenthe high resistivity material and the layers below it, for example thelower level copper interconnect. Second, the thicker the material, thehigher the resistance simply passing through the bulk of the highresistivity layer.

A solution, which would provide WN layers that result in an increase inits barrier effectiveness without an increase in its electricalresistance and an improvement in the texture of the overlying copperlayers, has long been sought, but has eluded those skilled in the art.As the semiconductor industry is moving from aluminum to copper andother type of materials with greater electrical conductivity anddiffusiveness through dielectrics, it is becoming more pressing that asolution be found.

DISCLOSURE OF THE INVENTION

The present invention provides a method for manufacturing asemiconductor device by forming: a conductive barrier layer on asemiconductor wherein said conductive barrier layer is a refractorymetal; forming a high barrier effectiveness barrier layer on said firstconductive barrier layer wherein said high barrier effectiveness barrierlayer includes a high resistivity metal; and forming a conductive layeron said second conductive barrier layer.

The present invention further provides a method for manufacturing asemiconductor device by: depositing a tantalum layer to line thechannels and vias of a semiconductor; depositing a tungsten nitridelayer at a low temperature on the tantalum layer; and depositing acopper conductor layer on the tungsten nitride layer. The tungstennitride acts as a highly efficient copper barrier material with highresistivity while the tantalum layer acts as a conductive barriermaterial to reduce the overall resistance. The low temperature isselected to be compatible with the low k dielectric of thesemiconductor.

The present invention further provides a method for forming barriermaterial layers and an associated structure with improved barriereffectiveness to copper diffusion.

The present invention provides a method for forming barrier materiallayers and an associated structure that has an improved texture in theoverlying copper layers.

The present invention provides a method for forming barrier materiallayers and an associated structure that can be deposited at lowtemperatures compatible with low k dielectric materials.

The above and additional advantages of the present invention will becomeapparent to those skilled in the art from a reading of the followingdetailed description when taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A (PRIOR ART) is a plan view of aligned channels with a prior artvia;

FIG. 1B (PRIOR ART) is a cross-section of FIG. 1A (PRIOR ART) along line2--2; and

FIG. 2 is a plan view of aligned channels with a via formed inaccordance with the present invention

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1A (PRIOR ART), therein is shown a plan view of aprior art pair of perpendicularly aligned semiconductor channels of aconductive material such as aluminum, copper, tungsten or polysilicondisposed over a production semiconductor wafer 100. A first channel 101is shown disposed below a second channel 102 which extends substantiallyperpendicular to the first channel 101 in the plan view. Similarly, around via 104 connects the first and second channels 101 and 102 and isa part of the second channel 102. The first channel comprises a firstconductive material. The second channel 102 is formed by filling asecond channel opening 106 disposed in a second channel oxide layer 108with a second conductive material.

Referring now to FIG. 1B (PRIOR ART), therein is shown a cross-sectionof FIG. 1A (PRIOR ART) along 2--2. The first channel 101 is disposedover a polysilicon gate 110 and a dielectric 112 of a semiconductordevice on an integrated circuit chip (not shown). The first and secondchannels 101 and 102 are in horizontal planes separated vertically by astop nitride layer 114, a via oxide layer 116, and a thin via nitridelayer 117. The cross-sectional area of the round via 104 of FIG. 1A(PRIOR ART) defines a cylindrical via 120 when it is filled with thesecond conductive material.

Also shown disposed around the first channel 101 is adhesion material121 and barrier material 122, and around the second channel 102 and thecylindrical via 120 is conductive adhesion material 123 and conductivebarrier material 124. Barrier materials, where necessary, are used toprevent diffusion of the conductive materials into the adjacent areas ofthe semiconductor. Titanium nitride, tantalum nitride, and tungstennitride are examples of barrier materials for copper channels.

The nitrogen component greatly increases the barrier effectiveness ofthe refractory metal over the pure metal, although it also increases itsresistivity. As previously explained, to improve the adhesion of thebarrier material to the underlying dielectrics, adhesion/barriermaterial stacks such as tantalum/tantalum nitride (Ta/TaN) andtitanium/titanium nitride (Ti/TiN) are used as adhesion/barrier materialcombinations for copper channels.

Where WN has been used in the past, no adhesion material has beenrequired or has been desired because WN adheres well to dielectrics,such as oxide and polysilicon. For purposes of clarity, theadhesion/barrier materials 121/122 and 123/124 are not shown in FIG. 1A(PRIOR ART).

WN is a desirable barrier material for copper interconnection because ithas satisfactory barrier effectiveness to copper. However, it isdifficult to optimize its barrier effectiveness by increasing itsnitrogen content since an increase in the nitrogen content leads to anundesirable increase in the electrical resistance of the barrier layer.Another problem with using WN as a barrier material layer has been thatthe crystallographic texture of the overlying copper layer tends to havea crystal orientation where the grains are not closely aligned, whichleads to poor resistance to electromigration.

Referring to FIG. 2, therein is shown the cross-section of asemiconductor wafer 200 with a pair of aligned semiconductor channels ofa conductive material, such as copper, disposed over a silicon substrate110 formed in accordance with the present invention. The presentinvention provides a method for forming an adhesion/barrier layer havinghigh barrier effectiveness and low resistivity. The adhesion/barrierlayer has a conductive barrier of Ta combined with a high nitrogencontaining WN layer. For convenience of illustration, like referencenumerals are used in FIG. 2 to denote like elements already described inFIG. 1. FIG. 2 is identical to FIG. 1 except that in this preferredembodiment, adhesion/barrier material stack 221/222 and 223/224 areformed of Ta/WN.

Unlike the conventional WN barrier layer which includes a nitrogencontent by atomic concentration of about 30% the WN barrier layer formedaccording to the present invention contains a nitrogen content by atomicconcentration of between 40% and 60%, and preferably between 45% and55%. Due to the increase in nitrogen content, the WN barrier layer 222and 224 has improved barrier effectiveness to copper diffusion. Eventhough the electrical resistance of the WN barrier layers 222 and 224have increased because of the higher nitrogen contents, the highelectrical conductivity of the Ta adhesion layers 221 and 223 offset theincrease in electrical resistance. Thus the Ta/WN adhesion/barriermaterial stacks 221/222 and 223/224 formed in accordance with thepresent invention have electrical resistance value comparable to thosefound in the conventional WN barrier material layer in which WN barrierlayer is used without an adhesion layer.

In addition, it has been determined that the texture of the overlyingcopper interconnection channels 201 and 202 have improved as a result ofthe use of Ta adhesion layers 221 and 223 underneath the respectivebarrier material layer 222 and 224. Accordingly, the present inventionprovides a method for forming a barrier layer which includes WN whichhas high barrier effectiveness compared to the prior art without anincrease in its electrical resistance and at the same time causingimproved texture in the overlying copper layers. This means that thecopper grains are closely aligned to the same crystal orientation andthus better resist electromigration.

In production, a conventional first damascene process was used to putdown over a production semiconductor wafer 200 a first channel 201 in afirst channel oxide layer (not shown) above portions of a semiconductordevice which is formed over a silicon substrate 110. The damasceneprocess is a photolithographic process which uses a mask to define afirst channel opening (not shown) in the first channel oxide layer torun in a first direction (which is horizontal in FIG. 1). The firstchannel opening is then lined with the barrier material of the presentinvention as will be described in detail for the second channel 202. Thefirst channel opening is then filled with a first conductive material toform the first channel 201 using conventional metal depositiontechnique, such as physical vapor deposition, chemical vapor deposition,electroplating, or a combination thereof The stop nitride layer 114, thevia oxide layer 116, and the via nitride layer 117 would be successivelydeposited on top of the first channel 201 and the first channel oxidelayer using conventional deposition technique.

By using the via photoresist and the via photolithographic processfollowed by nitride etching of a round via opening 104 in the vianitride layer 117, the basis for the cylindrical via 118 was formed. Thesubsequent deposition of the second channel oxide layer 108 prepares theway for the second channel 106 to be perpendicular to the first channel201.

The second damascene process is a photolithographic process which uses amask to define the second channel opening 106 in the second channeloxide layer 108. Since the second damascene process uses an anisotropicoxide etch, the etch also forms the cylindrical via opening 118 down tothe stop nitride layer 114. The anisotropic oxide etch etches faster inthe vertical direction of FIG. 1 than in the horizontal direction. Thenitride etch of the stop nitride layer 114 exposes a portion of thefirst channel 201 and completes the etching steps.

Thereafter, a thin layer of Ta adhesion material 223 is deposited in thesecond channel opening 106 and the cylindrical via opening 118,including along the walls of the second channel opening 106 and thecylindrical via opening 118. The thickness of the Ta adhesion material223 is lines the second channel opening 106 and the cylindrical viaopening 118.

Next, a thin layer of high nitrogen concentration WN barrier material224 is deposited in the second channel opening 106 and the cylindricalvia opening 118 and on top of the Ta adhesion material 223. Thepreferred process of deposition is chemical vapor deposition since itresults in better step coverage and conformality. A W-bearing precursor,such as WF₆, is caused to react with an N-bearing precursor, such as N,N₂, NH₃, or NF₃, with or without the aid of plasma. The high nitrogenconcentration permits the WN to be deposited at temperatures below 450°C. and even below 400° C. The WN barrier material 224 overlays the Taadhesion material 223 in the second channel opening 106 and thecylindrical via opening 118. The deposition of the WN barrier material224 is followed by the deposition of the second conductive material,such as copper, into second channel opening 106 and via opening 118 toform the second channel 202 and the cylindrical via 220.

The Ta adhesion material 223 is deposited using conventional depositiontechniques, such as physical vapor deposition, chemical vapordeposition, or a combination thereof. Similarly, the WN barrier material224 is deposited using conventional deposition techniques, such asphysical vapor deposition, chemical vapor deposition, or a combinationthereof.

The second conductive material is deposited using conventional metaldeposition technique, such as physical vapor deposition, chemical vapordeposition, electroplating, or a combination thereof. Thereafter, achemical mechanical polishing process is used to complete theconventional connection process.

In a preferred embodiment, the WN barrier layer contains a nitrogencontent by atomic concentration of between about 40% and 60%, andpreferably between about 45% and 55%, and has a thickness of between 20angstroms to 200 angstroms, and preferably between 50 angstroms to 100angstroms. The corresponding Ta adhesion layer has a thickness ofbetween about 10 angstroms to 200 angstroms, and preferably betweenabout 20 angstroms to 50 angstroms.

Accordingly, the present invention provides a method for forming WNlayers and an associate structure that have increased barriereffectiveness without an increase in its resistance and improved texturein the overlying copper layers.

While the best mode utilizes copper as the conductive material, itshould be understood that the present invention is applicable to otherhigh conductivity materials such as aluminum, doped polysilicon, copper,gold, silver, alloys thereof, and combinations thereof. Further,although the embodiments of the present invention are directed to usingTa as the adhesion material for WN barrier material, it also will berecognized by those skilled in the art that other refractory metals,such as titanium; refractory metal-containing materials; ortantalum-containing materials may be used to practice the presentinvention. Further, it is understood that a seed layer of conductivematerial may be deposited before the conductive material which fills thechannels and vias is deposited.

While the invention has been described in conjunction with a specificbest mode, it is to be understood that many alternatives, modifications,and variations will be apparent to those skilled in the art in light ofthe aforegoing description. Accordingly, it is intended to embrace allsuch alternatives, modifications, and variations which fall within thespirit and scope of the included claims. All matters set forth herein orshown in the accompanying drawings are to be interpreted in anillustrative and non-limiting sense.

The invention claimed is:
 1. A method of manufacturing a semiconductordevice, comprising the steps of:forming a conductive barrier layer on achannel in a semiconductor wherein said conductive barrier layer is arefractory metal; forming a high barrier effectiveness layer on saidconductive barrier layer wherein said high barrier effectiveness layeris a high resistivity barrier material and wherein said high barriereffectiveness layer contains a barrier dopant of between about 40% and60% by atomic concentration; and forming a conductive layer on said highbarrier effectiveness layer.
 2. The method as claimed in claim 1 whereinsaid steps of:forming said conductive barrier layer is performed using arefractory metal selected from a group comprising tantalum, titanium,tungsten, an alloy thereof and a combination thereof; and forming saidhigh barrier effectiveness layer is performed using tungsten and abarrier dopant.
 3. The method as claimed in claim 1 wherein said step offorming said high barrier effectiveness layer is performed at atemperature below 450° C.
 4. The method as claimed in claim 1 whereinsaid step of forming said conductive barrier layer is done by adeposition process selected from a group comprising physical vapordeposition, chemical vapor deposition, and a combination thereof.
 5. Themethod as claimed in claim 1 wherein said step of forming said highbarrier effectiveness barrier layer is done by a deposition processselected from a group comprising physical vapor deposition, chemicalvapor deposition, and a combination thereof.
 6. The method as claimed inclaim 1 wherein said step of forming said conductive layer is performedusing a material selected from a group comprising aluminum, dopedpolysilicon, copper, gold, silver, an alloy thereof, and a combinationthereof.
 7. A method of manufacturing a semiconductor device, comprisingthe steps of:forming a conductive barrier layer on a channel in asemiconductor wherein said conductive barrier layer is selected from agroup comprising tantalum, titanium, tungsten, an alloy thereof and acombination thereof; forming a high barrier effectiveness layer on saidconductive barrier layer wherein said high barrier effectiveness layeris tungsten nitride material and wherein said high barrier effectivenesslayer contains nitrogen of between 45% and 55% by atomic concentration;and forming a conductive layer on said high barrier effectiveness layer.8. The method as claimed in claim 7 wherein said step of forming saidhigh barrier effectiveness layer is performed at a temperature below400° C.
 9. The method as claimed in claim 7 wherein said step of formingsaid conductive barrier layer is done by a deposition process selectedfrom a group comprising physical vapor deposition, chemical vapordeposition, and a combination thereof.
 10. The method as claimed inclaim 7 wherein said step of forming said high barrier effectivenessbarrier layer is done by a deposition process selected from a groupcomprising physical vapor deposition, chemical vapor deposition, and acombination thereof.
 11. The method as claimed in claim 7 wherein saidstep of forming said conductive layer is performed using a materialselected from a group comprising aluminum, copper, gold, silver, analloy thereof, and a combination thereof.